We are developing a new family of molecular wheels to be integrated in nanovehicles.
- The two wheels-and-axle molecule is pushed by the tip apex (in grey) of the STM on a copper surface.
- © CEMES-CNRS
The use of wheel rotational motions around an axle has led to the conception of mechanical machineries with multiple gearings, followed by engines and ultimately the industrial revolution. Reaching the nanometer size, which is the smallest possible for a wheel, represents a great challenge for chemists and physicists. In the past years, we work on the design and synthesis of molecules-machines equipped with wheels. Step by step, we have been pioneers in this field, together with colleagues at the Fritz-Haber institut in Berlin (Dr Leonhard Grill). The originality of their approach lies in containing the studies to one molecule only, chosen among a number of congeners, deposited onto a metallic surface. With its ultrafine tip which is stabilized 1 nm above the surface by an electric current induced by tunnel effect, the scanning tunneling microscope (STM) yields a cartography of the molecules present on the surface. This tip also enables researchers to manipulate the molecules one by one in order to study their mechanical properties.
After the synthesis and observation of a wheelbarrow molecule in 2005 (a molecule composed of a rigid board, two legs ad two wheels), researchers have shown in 2007 that when two wheels are mounted on an axle, one of them is able to rotate under the push of the STM tip. They succeeded in controlling the direction of the rotation, which opens the way to the synthesis of functional nanovehicles. Experimentally speaking, the molecules were carefully deposited onto a very clean copper surface, and observed by the means of an STM. The STM tip is used both as a probe to capture an "image" and as a nano-sized finger to trigger the the rotation of the wheel, being placed in the perfect position for that purpose (see figure).
- Macroscopic wheelbarrow and its molecular homologue (3 x 2 nm)
- © CEMES-CNRS
Such weels have an intrinsic drawback, having three sharp blades instead of a smooth "tyre". We are currently developing a new family of rigid wheels, of circular shape and curved, so as to minimise the mechanical interactions with the surface while increasing the rigidity of the architecture. These results open the way to the creation of mechanical molecules-machines, with the long-term objective to embark on a single molecule all the machinery required to achieve a nano-car (wheels, chassis and engine), in order to be able to transport matter in the nano-world.
Recently, we have synthesized polycyclic aromatic hydrocarbons nanovehicles designed by analogy with macroscopic vehicles. The synthesis of two new chassis has been achieved, both including a dedicated cargo zone.
- A molecular vehicle of a few nanometers superimpozed with a macroscopic car.
- © G. Rapenne CEMES, CNRS/UPS
Work is now underway to image and manipulate the molecular nanovehicles with an STM tip, and in particular the possibility to load the cargo zone with, for instance, co-deposited C60 molecules which would have a good affinity for such aromatic structures.
-  Synthesis of technomimetic molecules : Towards rotation control in single molecular machines and motors G. Rapenne, Org. Biomol. Chem. 2005, 3, 1165-1169. Download
-  Rolling single “nano-wheels” with the STM tip L. Grill, X. Bouju, G. Rapenne, S. Stojkovic, C. Joachim, K.-H. Rieder, F. Moresco, Nature Nanotech. 2007, 2, 95-98. Download
-  Molecular Machines : Synthesis and characterization of two prototypes of molecular wheelbarrows G. Rapenne, G. Jimenez-Bueno, Tetrahedron 2007, 63, 7018-7026. Download
-  Synthesis of polycyclic aromatic hydrocarbon-based nanovehicles equiped with triptycene wheels. H.P. Jacquot de Rouville, R. Garbage, R.E. Cook, A.R. Pujol, A.M. Sirven, G. Rapenne, Chem. Eur. J. 2012, 18,3023-3031. Download
-  Synthesis and STM-imaging of symmetric and dissymmetric ethynyl-bridged dimers of boron-subphthalocyanine bowl-shaped nano-wheels. H.P. Jacquot de Rouville, R. Garbage, F. Ample, A. Nickel, J. Meyer, F. Moresco, C. Joachim, G. Rapenne, Chem. Eur. J. 2012, 18, 8925-8928. Download
-  Molecule concept-nanocars : chassis, wheels and motors ?
C. Joachim, G. Rapenne, ACS Nano, 2013, 7, 11-14. Download
CNRS, EU, ANR, IUF, Université de Toulouse.